This invention relates generally to a vacuum holding system including a table having a workpiece engageable surface comprised of contiguous vacuum zones, and deals more particularly with a valve through which one or more of the vacuum zones in such a system are energized.
In the general type of vacuum system with which this invention is concerned, a vacuum table includes a workpiece engageable surface divided into contiguous vacuum zones. Each of the vacuum zones are in communication with a vacuum source through individual conduits, and valves are installed in the conduits to permit an operator to energize the zones individually. Examples of vacuum holding systems such as aforedescribed are embodied in sheet material holddown tables disclosed in U.S. Pat. Nos. 3,495,492 and 3,848,327. The number of conduit valves in each of these general types of systems is equal to the number of vacuum zones in the table and may represent a high proportion of the total cost of the holding system.
If the table in the system is mounted for movement in one or more coordinate directions relative to a fixed structure by means of a drive motor, it is desirable that the table be as light as possible because less power is required by the drive motor to move the table and there is less likelihood of positioning errors due to inertia effects. If several valves are carried by the table to effectuate the communication between the individual vacuum zones and the vacuum source, the table is necessarily heavy. If the valves are mounted off of the table, then the movement of multiple conduits with the table presents another problem.
Typically, the vacuum zones arranged adjacent one another on the surface of a contiguously-zoned table are progressively energized or de-energized to increase or decrease the effective holding area of the table surface. However, if one table zone which is desired to be energized in progression with adjacent zones fails to be energized due to valve failure or mere inadvertance, the fact that the zone is not energized may not be detected for some time.
It is accordingly an object of this invention to provide a single valve for use with a contiguously-zoned vacuum table for energizing one or more of the vacuum zones of the table.
It is a further object of this invention to provide a single valve suitable for attachment to a movable vacuum table in place of the several valves or multiple conduits carried by the table in the prior art and thereby reduce the weight of the table.
It is a still further object of this invention to provide a valve which allows an operator to reliably energize or deenergize in progression the vacuum zones of a contiguously-zoned vacuum table to increase or decrease the effective holding area of the table surface.